Continuity mistake: When "Lex" threatens the bank manager, he points the gun at his face, but the next shot on the manager shows the gun at his throat. (00:01:35)
Continuity mistake: Tina's grip on Lana's necklace changes as she stands over Lana's body. (00:37:30)
Factual error: Lana says the theme of her mother's prom was Saturday Night Fever, but she was in the class of 1977. Prom would take place sometime before graduation (which would be in May, maybe June), likely February or March. Filming for "Saturday Night Fever" didn't even begin until March 1977.
Revealing mistake: While Lana is listening to her Mother's graduation speech she reaches up to her neck for her meteor rock necklace. Her hands do not reach far enough back to unclasp the necklace yet the necklace comes off anyway.
Revealing mistake: As Tina/Clark tries to run over Martha, there is a shot of Tina/Clark up close in the truck, and the gear shift is still in park.
Visible crew/equipment: After Martha finds the money in the antique shop she tells the other woman she needs to be more careful, as they are walking in the room there is a boom mike shadow moving.
Answer: The kryptonite only creates mutations when it reacts with the environment and an individual. Remember, the FDA and several environmental groups did check out Smallville after the meteor shower, but found no danger in the rocks. Obviously they're not always emitting mutating rays, or all the flora and fauna of the surrounding area would be horribly mutated.
Phoenix